The effect of amphetamine on the average evoked response (AER) is being studied in hyperactive children. Blood amphetamine levels will be correlated with AER measures in an attempt to understand individual differences in response. The AER is only one phase of a larger project reported elsewhere. In an effort to demonstrate possible response stereotypy associated with amphetamine, single evoked response trials are being collected for both visual and auditory stimuli. These single trials are then being analyzed for signal/noise ratio and trial-to-trial similarity using newly developed signal processing techniques.